TCP Flow Control
How the receive window limits data in flight.
A TCP receiver advertises a receive window indicating how much data it can accept. The sender uses that window to limit unacknowledged data and avoid overflowing the receiver’s buffer.
Flow control protects the receiver; congestion control limits pressure on the network. A sender must respect both the receive window and the congestion window.
When the receive window reaches zero, the sender pauses ordinary data transmission and periodically probes for an update. This lets transmission resume even if a window-update message was lost.